1. Field of the Invention
The present invention relates to a stable medium, which is particularly useful in topical applications and which contains an active agent which is sensitive to water. Such compositions are particularly useful in the cosmetic and/or dermatological fields for cleansing and/or caring for and/or protecting the skin and/or keratinous fibers.
2. Description of the Background
It is known to prepare cosmetic and/or dermatological compositions containing active agents which confer specific effects to the skin and/or hair, for example to cleanse the skin, to combat drying, ageing or pigmentation of the skin, to treat acne or some skin diseases (eczema, psoriasis), to combat overweight, to promote the restructuring of the skin or its cellular renewal or to treat seborrhoea of the hair. For example, ascorbic acid (or vitamin C) is known to stimulate the growth of the connective tissue, especially that of collagen. It also strengthens the defense of cutaneous tissue against external aggressive agents such as ultraviolet radiation and pollution. It is also used to remove spots and pigmentation from the skin and also to promote cicatrization of the skin.
It is also known to introduce enzymes into cosmetic compositions, especially proteases for their proteolytic properties. These enzymes are in great demand in the cosmetic field for their smoothing and cleansing power, and for their capacity to remove dead cells from the skin.
Unfortunately, these active agents, as well as others, have the disadvantage of being unstable in aqueous media and of being easily degraded or modified under the influence of water. They thus rapidly lose their activity over time and this instability runs counter to the desired efficacy.
Accordingly, various proposals have been made to overcome these disadvantages. One proposal has been to place an active agent, especially an enzyme, in a pulverulent composition (JP-A-63-130514). Most of the skin cleansing products containing an enzyme exist in this form. It has also been proposed to use these active agents, especially enzymes, in a form in which they are immobilized on polymeric supports (JP-A-61-207499) or in microcapsules (JP-A-61-254244). Unfortunately, some of these techniques require special operations, which increase the cost and the time for preparing the compositions.
Another proposal is the incorporation of the components in an anhydrous liquid medium (U.S. Pat. No. 5,322,683). Unfortunately, this solution limits the galenic form of the composition and does not allow the incorporation of hydrophilic active agents. A need therefore continues to exist for a stable medium which contains hydrophilic and/or lipophilic cosmetic and/or dermatological active agents which are sensitive to water, the active agents retaining all their properties and therefore their efficacy over time.